Coating composition and article coated with same

ABSTRACT

An emulsion coating composition and a substrate coated therewith. The aqueous phase of the coating contains a blend of resinous materials, one resin component, such as casein, forming a matrix structure and the other, such as an acrylic polymer, forming an essentially continuous film. The coating after drying contains small air-binder interfaces which scatter light. The resin components making up the binder may be chosen to give the coating a wide range of physical and chemical properties.

United States Patent Brenneman et al.

1451 Jan. 25, 1972 [54] COATING COMPOSITION AND 3,157,533 11/1964 Clancyet al. ..117/164 x 3,306,763 2/1967 Hoge ...1 17/155 X ARTICLE COATEDWITH SAME 3,328,184 6/1967 Weber. ..1 17/164 X [72] Inventors: RichardS. Brenneman, Natick; John J. 3,347,702 10/1967 Clancy ..117/36.7 XClancy, Westwood; William T. MacLeish, 3,372,044 3/1968 Weber 117/164 XAndover; Robert C. Wells, Arlington, all 3,399,060 10/1968 Clancy"117/201 X ofMass. 3,497,380 2/1970 Weber ..117/161 UX [73] Assignee:Arthur D. Little, Inc., Cambridge, Mass. I Primary Examiner wimam D M am[22] Fil d; S t 30, 1963 Assistant Examiner-M R. LusignanAttorney-Bessie A. Lepper [21] Appl. No.: 763,884

[57] ABSTRACT [52] U.S.Cl ..117/155 UA, 117/156 An emulsion coatingcomposition and a Substrate coated [51] Int. Cl ..D2lh l/38, D21h l/34therewith The aqueous phase of the coating contains a blend [58] new ofSearch "117/111 155 UA, 161 161 of resinous materials, one resincomponent, such as casein, 117/161 156 forming a matrix structure andthe other, such as an acrylic polymer, forming an essentially continuousfilm. The coating [56] Reerences after drying contains small air-binderinterfaces which scatter light. The resin components making up thebinder may be UNITED STATES PATENTS chosen to give the coating a widerange of physical and chemi- 2,759,847 8/1956 Frost et al ..117/164 Xcal properties. 2,961,334 11/1960 Clancy et a1. ...1 17/164 X 3,028,2584/1962 Rice ..1 17/156 x 13 Clam, 4 Drawing 3,108,009 10/1963 Clancyetal, l l7/ 164 X o l2 l0 b PATENTEBJANZSIHYZ 3 5 7 Fig.3

Fig.

Richard S. Brennemcin John J. Clancy William T. MucLeish Robert C. WellsINVENTCRS life rn e COATING COMPOSITION AND ARTICLE COATED WITH SAMEThis invention relates to a novel coating and to substrates coated withit. More particularly, this invention relates to a novel, opaque coatingwhich is essentially water-insensitive and which may have modifiedsurface characteristics including sensitivity or insensitivity topressure, printing strength, ink receptivity and the like.

Many surfaces require one or more coatings for decoration, protection,or modification of their physical characteristics. For example, paint isused to decorate and protect walls, woodwork and the like; highlypigmented coatings are applied to paper and paperboard to cover theirsurfaces with a base coating to which further decorations and printingmay be applied; and opaque coatings which are pressure sensitive to apredetermined degree are applied to colored, normally lightweight,papers to make a surface which may be marked by application of pressurealone.

In recent years there has been developed a new technology in the coatingart which has come to be referred to generally as bubble coatingtechnology, a term which will hereinafter be used to describe a coatingcomposition, a method of application and a coating, the final structureof which comprises an essentially continuous binder film havinguniformly distributed throughout minute air-binder interfaces whichcause the scattering of light. The presence of these air-binderinterfaces gives rise to the use of the descriptive but rather generalterm bubble coating. Because the coating in its unique physical formdevelops desired optical properties, it need not contain any of theusual pigment materials such as titania chalk, clay and the like. Thisin turn materially reduces coating weight for a given degree ofbrightness and opacity. However, this coating composition and theresulting coating may contain relatively large quantities of finelydivided particulate material for a number of different purposes such asink receptivity, ease of application of the liquid coating, ease ofdrying, and additionally desired optical effects.

The prior art of bubble coating is represented by five U.S. Pat. Nos.2,961,334, 3,108,009, 3,157,533, 3,347,702 and 3,399,060. In addition acopending application Ser. No. 638,520 now abandoned and refiled as Ser.No. 881,693 filed in the names of Richard S. Brenneman, John J. Clancyand Robert C. Wells is directed to an improvement of the coatingcomposition and method of U.S. Pat. No. 3,108,009 to provide ahigh-gloss coating which has good reflectivity and printing properties.

In this prior art there is disclosed first in U.S. Pat. No. 3,108,009 abasic coating composition, method of application and coated substrate inwhich a proteinaceous material, specifically casein or soya proteinforms the film structure containing the air-binder interfaces. Asynthetic or natural rubber may be used to replace some of theproteinaceous film forming binder material. The coating preparedaccording to the teaching of this invention is extremely bright andopaque. It can be formed to be controllably pressure sensitive within alimited range and may incorporate finely divided particulate material toattain certain desirable surface characteristics. U.S. Pat. No.3,157,533 teaches that the addition of starch to the basic formulationmaterially enhances its ease of application to a substrate andcontributes desirable properties to the finished coating. Copendingapplication Ser. No. 638,520 discloses that a small amount of afilm-forming thermoplastic resin may be added to give a bubble coatingwhich is receptive to a unique succession of treating steps to form ahigh-gloss coating.

An improvement of the basic coating composition, method and articledescribed in U.S. Pat. No. 3,108,009 is set forth in U.S. Pat. No. 2,961,334 which teaches the incorporation of a relatively large quantity of aso-called "transparentizing agent to render the finished coating highlysensitive to pressure thus making it a lightweight coating particularlysuitable for making multiple copies by application of pressure withoutthe use of carbon paper. The film formers in this composition,

in addition to casein, soya protein and mixtures of these with rubbers,are such water-sensitive materials as polyvinyl alcohol, glue, modifiedstarches, sodium silicate, methyl cellulose, ethyl cellulose andshellac.

Finally, U.S. Pat. Nos. 3,347,702 and 3,399,060 teach the application ofthe bubble coating technique to the formation and use ofelectrophotographic coatings and copy papers.

It will be seen that the film-forming materials in the prior art havebeen limited to proteinaceous materials with or without particulateadditives, and to a relatively restricted number of water-sensitivematerials. Although elastomers, i.e., natural or synthetic rubbers, maybe used, they are not ideally suited to contributing additionallydesired properties such as precise control of pressure-sensitivity,water-insensitivity, resistance to weathering, and the like. Moreover,although the use of large quantities of a transparentizing agent makesthe bubble coating highly sensitive to pressure, its presence may beundesirable, particularly in applications where high-speed printing is arequirement.

Despite numerous attempts to extend the bubble technology tononelastomeric synthetic resins (i.e., those which did not exhibit amaterial degree of elasticity such as the natural and synthetic rubbersdisclosed in U.S. Pat. No. 2,96l,3 34, 3,108,009 and 3,157,533) in orderto obtain the advantages inherent in the tailor-made" properties of suchsynthetic resins, difficulties were continually encountered in theiruse. In general these difficulties were exhibited in an inability toform them into the desired bubble structure to achieve efficient use ofmaterials or to attain a permanent degree of opacity in the coating madewith them. We have now, however, discovered that by using a blend ofwhat may for convenience be termed hard" or matrix structure-forming"and soft" or film-forming" components, it is possible to extend bubbletechnology to the use of synthetic resins, thus making an entirely newclass of bubble coatings available for such diverse uses aspressure-sensitive coatings markable by pressure alone which take theplace of carbon paper, printing or publication papers and indoor andoutdoor paints.

It is, therefore, a primary object of this invention to provide animproved coating composition suitable for use in bubble coatingtechnology. It is another object of this invention to provide a coatingcomposition of the character described which makes it possible to use anonelastomeric resin as at least one of its binder-forming constituents.It is another object of this invention to provide a bubble coatingcomprising at least one nonelastomeric synthetic resin component, thecomponent being chosen to impart to the coating a wide range of physicalproperties. It is another primary object of this invention to provide acoating of the bubble type which exhibits a sensitivity to pressure fromessentially zero to being highly sensitive. It is yet another object ofthis invention to provide among other articles a new improvedpressure-sensitive coating for paper which exhibits good printingstrength. Other objects of the invention will in part be obvious andwill in part be apparent hereinafter.

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others, and thearticle possessing the features, properties and the relation of elementswhich are exemplified in the following detailed disclosure, and thescope of the invention will be indicated by the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which FIG. 1 is adiagrammatic cross-sectional representation of the coating compositionof this invention immediately after application to a substrate;

FIG. 2 is a diagrammatic cross-sectional representation of the coatingof FIG. 1 after at least a portion of the water is removed;

FIG. 3 is a diagrammatic cross-sectional representation of the finallydried coating; and

FIG. 4 is a cross section of a modification of a coated substrateshowing an intermediate layer.

In bubble technology, the basic coating composition is comprised of anoil-in-water emulsion, the oil phase being dispersed in the form ofglobules within a size range which corresponds essentially directly tothe size of the air-binder interfaces formed in the final coatings.Normally, for maximum lightscattering and hence maximum opacity, theseinterfaces are of a size such that their maximum dimensions are aboutequal to the wavelength of the visible light range of theelectromagnetic spectrum. This means then that essentially all of thewater-immiscible globules making up the oil or discontinuous phase ofthe coating emulsion will range from about onetenth to 1 micron. It ispreferable that no appreciable number exceed 5 microns if high opacityand efficient use of coating materials are sought. The film-formingbinder material is dissolved or dispersed in the continuous aqueousphase while additives such as emulsifiers, pigments, other particulatematerial, dyes, etc., may be dissolved or dispersed in either or both ofthe two liquid phases forming the emulsion.

The emulsion coating is applied to the surface of the substrate in amanner to retain the original emulsion structure. The water-immisciblediscontinuous phase is chosen to have a boiling point above water (e.g.,kerosene, xylene and the like) so that as drying begins the water of thecontinuous phase is volatilized first. With the removal of at least aportion of the water, the film-forming binder material sets up into amatrix structure in which the water-immiscible liquid globules areentrapped, thus maintaining the relative spatial relationship of theglobules with some decrease in actual coating thickness. Continueddrying then efiects volatilization of the water-immiscible liquid fromthe matrix with the formation of the airbinder interfaces throughout thefilm structure which is stabilized in its unique form. Thus in the priorart the casein or soya protein binder material played the dual role ofmatrix structure-former and film-former.

It is believed that single-component synthetic resin-binder systemsfailed in the requirement to be able to establish a stable permanentmatrix structure prior to the removal of the discontinuous phase liquid,or to be able to maintain this structure without collapsing once thediscontinuous phase liquid was finally removed. Thus the syntheticresins which are capable of imparting completely new properties tobubble coatings or of enhancing the present properties of these coatingscould not be used effectively.

In practice of this invention these restrictions on the use of syntheticresins are overcome by forming the binder material of at least twocomponents, one contributing substantially to the initial formation andthe other to the final formation of the required bubble structure. Thebinder materials are, therefore, formed of a blend of components. Onecomponent is essentially a structure-forming material and it may or maynot be a film-forming synthetic resin at the drying temperature. Itmust, however, be capable of setting up into a matrix structure as thewater of the continuous phase of the emulsion is removed from theapplied coating. The other component is a film-forming synthetic resinwhich builds the necessary essentially continuous film around the matrixstructure upon the removal of the water-immiscible liquid discontinuousphase. Such a blend permits a wide selection of film-forming resins togive the final coating its desired physical properties while maintainingthe optical properties associated with the bubble structure.

The blends usable fall into three general classes which may be definedas l. a physical blend of a matrix structure-forming resin and afilm-forming resin, each of the resins being dissolved or dispersed inthe aqueous phase,

2. a chemical blend in which two different resin components arecopolymerized, one component contributing to the formation of the matrixstructure, the other to the formation of the film. The copolymer may besoluble or dispersible in the aqueous phase, and

3. a physical blend of a matrix structure-forming resin dissolved ordispersed in the aqueous phase and a coalescing agent for the resindissolved or dispersed in the aqueous phase or dissolved in thediscontinuous phase.

Although it is possible to delineate the types of blends into thesethree general classes, in many instances a coating composition maycontain more than one class of blend in order to obtain the desiredphysical characteristics in the final coating. Thus a portion of thematrix structure-forming resin system may be derived from a single resinand a portion from a copolymer, the copolymer furnishing all or part ofthe filmforming component.

FIGS. 1-4 are presented to describe the coating emulsion and structure.These figures are entirely diagrammatic and are not meant to be taken asan actual representation of a cross section of the coating or coatedsurface. However, it is believed that they can be used by way ofexplanation of what is believed to be taking place during applicationand drying of the coating.

In FIG. 1 the coating 10 is applied to the substrate 1]. The coatingcontains in its aqueous phase a matrix structure-forming resinrepresented by the solid lines 12, a film-forming resin represented bythe dashed lines 13 and small globules 14 of a water-immiscible liquidas the discontinuous phase. Finely divided particulate material 15 mayalso be present.

As the water from the continuous phase is removed the matrixstructure-forming resin sets up as represented by the heavy solid linesin FIG. 2 to give a partially dried coating 100. Then as more water isremoved and the discontinuous phase liquid is driven off thefilm-forming material also sets up as represented by heavy lines 13a,the binder system 16 takes form and the air-binder interfaces 17 whichscatter light are formed, giving rise to a permanent bubble" coating10b.

In FIG. 4 a modification of the coated article is shown in which acolored layer 18 is interposed between the bubble coating 10b and thesubstrate 11.

The following examples are set forth to illustrate more clearly theprinciple and practice of this invention to those skilled in the art andare not to be construed as limitations on the invention. The threeclasses of blends are illustrated as well as the wide range ofapplication for the coatings.

Examples 1-9 illustrate the first class blends, i.e., the physicalblending of two resins, each serving primarily in one of the two rolesdescribed.

EXAMPLE 1 A nonfilm-forming polyvinylchloride copolymer latex (56percent solids) sold as Geon 351 by B. F. Goodrich Company was used asthe harder matrix structure-forming resin and a film-forming vinylchloride-acrylate copolymer latex (53 percent solids) sold by B. F.Goodrich Company as Geon 450x23 was used as the softer film-formingresin component. The latices were first combined and then ll2 parts byweight of a petroleum fraction (distillation range between 205and 258C.) was added with mechanical stirring. The resulting emul sions werecoated on contrast ratio charts with an applicator blade at the rate ofapproximately 400 square feet per gallon. The coatings were allowed toair dry overnight and the reflectances of the coatings over the blackbackground were measured using a green filter. The reflectance for threecoatings containing three different ratios of the harder to softerresins were as follows:

Harder, nonfilm-forming resin 75 67 50 Parts by weight Softer,film-forming resin 25 33 50 Parts by weight Reflectance 67% 40% 0% Inthe evaluation of the bubble coatings, percent reflectance of astandard-weight coating is contains as a measure of the efficiency ofthe coating. It is a measure of brightness and is obtained by directmeasurement using a commercially available reflectometer or brightnessmeter. Reflectance values below about 40 percent for application weightsof about 400 square feet per gallon are considered as indicative of theinability of the coating composition to form' a desirable bubblestructure. Thus from these reflectance data it will be seen that thebinder system in the bubble coating requires a sufficient quantity of amatrix structure-forming resin to form and retain the bubble structure.

EXAMPLE 2 Two acrylic polymer latices were used in the binder system ofthis example, the first was nonfilm-forming (45 percent solids) whichgave a hard brittle polymer upon drying (sold as Rhoplex 072 by Rohm &Haas Company) and the second was a film-former (46 percent solids) whichgave a soft polymer upon drying (sold as AC-33 by Rohm & Haas Company).ln formulating the coating compositions, 1 part ammonium hydroxide (29percent N11 was added to 100 parts of the latex mixture and then 1 partof a partial amide of a vinyl methyl ether-maleic anhydride copolymerwas added as a thickening agent and to promote better wetting of thesubstrate to which the coating is applied. Finally 90 parts of analiphatic hydrocarbon blend (distillation range of 177 and 187 C.) wasadded with stirring to form the emulsion which was subsequently refinedto the extent that the oil globules were in the size range between about0.4 and 1 micron.

The coating compositions with varying resin ratios were applied to blackcardboard at the rate of approximately 400 square feet per gallon. Thecoatings were air dried overnight and then reflectance measurements(using a green filter) were made with the following results for threedifferent coatings:

Hard. nonfilm-forming resin 75 72.5 70 Parts by weight Softer.film-forming resin 25 27.5 30 Parts by weight Reflectance 51% 49% 54%All of these compositions therefore formed a bubble structure.

A number of other resin mixtures were evaluated using a basicformulation in which one part of binder and two parts of a liquidaliphatic hydrocarbon (having a distillation range between 205and 258C.) with sufficient water to give a desired viscosity formed theemulsion. Emulsifying and solubilizing agents were used in small amountswhere required and the formation of the liquid coating composition wascarried out as described in example 2. A number of the resin bindermixtures were made up using a range of resin components. Reflectanceswere determined for all the coatings formed, and these data aretabulated below.

Weight Percent ratio reflec- Exarnple Matrix structure- Film-forming of(1) tanee of Number forming resin (1) resin (2) to (2) coating 8 CaseinAeryliepolymerk. 10/90 20 do do. /85 67 do do 80 80 onium salt do. 5/9513 of an acrylic synthetic resin EXAMPLE l0 Pressure-sensitive bubblecoatings for pressure marking without the use of carbon paper were madeby dissolving 60 parts of a styrene-maleic anhydride resin (sold asLytron 822 by Monsanto Company) in an ammoniacal water containing 420parts water and 20 parts ammonium hydroxide (29 percent NH at 38 C. Analiphatic hydrocarbon having a distillation range between 160and 182 C.was emulsified into the aqueous phase with stirring and the emulsion wasrefined at 1,500 p.s.i.g. in a Manton-Gaulin l-lomogenizer. The coatingwas applied to a black precoated IO-pound register bond (l7 2 2 -50Qbasis) at a level of 1.2 pounds per ream with a No. 18 wire-wound rod.

The coated sheet had a 72 percent brightness or reflectance and producedsix excellent copies on an IBM typewriter. However, the [GT pickresistance was less than feet per minute with a No. l Tack Rated Ink andthe coated sheet had a relatively low resistance to scuff and abrasion.Although this coating with a high sensitivity to pressure would beuseful for chart paper and the like where it would receive minimumhandling, it would not be desirable for manifold business forms, etc.

EXAMPLE 1 1 In order to improve the pick resistance and abrasionresistance of example 10, a higher molecular weight resin similar to thestyrene-maleic anhydride resin of example 10, was substituted for theresin of example 10. The formulation, prepara- 'tion and use in thisexample was similar to example 10 except EXAMPLE 12 A styrene-acrylatecopolymer was substituted for the copolymer of example 10. The copolymerwas a latex sold under the trade name Lytron 100 by Monsanto Company.The reflectance of the resulting coating was 54 percent.

EXAMPLE 13 A vinyl chloride-acrylate copolymer latex (sold as Geon450x20 by B. F. Goodrich Company) was substituted for the copolymer ofexample 10. The resulting coating structure collapsed and had areflectance of zero percent. Although the precise ratio of vinylchloride to acrylate monomers is knot known, it is evident that thiscopolymer did not have a sufficient matrix structure-forming content.This is readily discernible from the physical properties of the polymeras described below.

In many coating compositions it is desirable to obtain the desiredbinder system by combining the first and second classes of blends. Suchcombinations are illustrated in examples 14-17.

EXAMPLE 14 A pressure-sensitive copy paper for use in multiple partforms was prepared by coatingabubble emulsion on a colorg base stock.The resulting highly opaque coating isiransparentized under thelocalized pressure exerted by writing or typing to reveal the coloredsubstrate.

The coating composition was formulated in the following manner, allamounts of ingredients being expressed as parts by weight. An ammoniawater solution was formed by mixing 11 parts ammonium hydroxide (29percent NH;) and 280 parts water. This solution was heated to 32 C. and8.4 parts of a styrene-maleic anhydride resin (sold as Lytron 810 byMonsanto Company) was dissolved in it. The resulting resin solution wasthen blended with 250 parts of a resin latex containing 40 percentsolids. The latex was a homogeneous blend of an emulsion polymerizedstyrene homopolymer latex containing as the sole emulsifier a salt of apartial ester of a styrene maleic anhydride copolymer and an emulsionpolymerized styrene interpolymer latex (see US. Pat. No. 3,396,135 for adetailed description of this type of latex). The styrene portion ofthese resins provided the matrix structure-forming component of thebinder and the maleic anhydride resins along with the monomer combinedwith the styrene to form the interpolymer provided the film-formingcomponent.

An aliphatic hydrocarbon liquid with a distillation range between l8land277 C. was used as the discontinuous oil phase in forming the emulsion.To 188 parts of this liquid was added 0.6 parts of oleic acid as anemulsifying agent. The liquid hydrocarbon containing the emulsifier wasemulsified in the aqueous blend of resins with slow speed agitation. Thecrude emulsion was refined to the correct particle size for maximumhiding power in a Manton-Gaulin Homogenizer, i.e., to reduce the size ofthe hydrocarbon liquid globules to between about one-tenth and 1 micron.The emulsion had a [5 percent solids content, a viscosity of 500 c.p.s.at 90 F., and a resin-to-oil ratio of l to 1.75.

This composition was coated on a base stock colored one one side. Thebase stock was a l2-pound (l7X22500 basis) register bond paper which wascoated on one side with a blue tinted clay coating at a coating weightof 1% pounds per ream. The bubble coating was applied to the bluecolored side of the paper with a wire-wound rod coater at a level of 1%pound per ream (l7X22-500) and dried in a festoon drier.

The resulting product was free from curl and had a 72 percent brightnessas measured on a Photovolt Brightness Meter. Business forms were printedand collated on a commercial web-offset press. The printed formsproduced four excellent copies when typed on by an IBM Executivetypewriter at pressure five.

EXAMPLE The pressure sensitivity ofa copy paper such as that formed inexample 14 may be enhanced to produce more copies on a typewriter or toform a product suitable for use for high-speed computer printout.High-speed impact printers, such as the IBM 360-30, print with much lesspressure and time of contact than typewriters and thus they require thatthe copy papers be more pressure-sensitive. increased sensitivity inthis coating was obtained by adjusting the ratio of matrixsturcture-forming resin to film-forming resin. The emulsion coatingcomposition was prepared by first blending l0.8 parts of thestyrene-maleic anhydride resin of example 10, 338 parts of water, 16parts ammonium hydroxide, 400 parts of the resin latex of example 14 and250 parts of a water dispersion of an ammonium salt of a synthetic resincomplex (22 perc ent TABLE I.COMPARISON OF EXAMPLE COMMERCIALLYAVAILABLE the aqueous phase with slow-speed stirring. The emulsion washomogenized to obtain a particle size of about one-half micron.

The emulsion was coated on a l2-pound l7 22500 basis) paper which wasprecoated one side with a clay-carbon black base coat. The coating wasapplied with a No. 24 wire-wound rod at a level of 1% pounds per reamand drying was accomplished as in example 14.

The coated product had a 75 percent brightness. Printing strength asmeasured on an IGT Print Tester was 500 feet per minute using a No. 1Jack-Rated Ink. The product produced three legible copies when printedon an IBM 360-30 printer. In comparison, the copy paper of example 14barely produces one legible copy using the 360-30 printer.

Example 16 Bubble coatings, based upon the proper blend of syntheticresins, are useful for papers designed for printing applications. Thesecoatings are relatively pressure insensitive and may be supercalenderedto provide a smooth, strong, printable surface on a paper having highopacity and brightness. Such a coating was prepared as follows to havegood printing characteristics. One hundred and thirty-six parts of adelaminated kaolin (sold as NuClay by Freeport Kaolin Company) and 14parts of anatase grade titania were dispersed in 504 parts of water. Thepurpose of these finely divided particulate materials is to contributephysical characteristics to the final coating and not to act primarilyas pigments in the usual sense, i.e., to improve optical properties. Tothis water dispersion were then added 22 parts of the sytrene-maleicanhydride resin of example 10, 30 parts of ammonium hydroxide, and 100parts of a styrene-butadiene latex (48 percent solids) sold by the DowChemical Company as Dow Latex 636. This aqueous phase blend was heatedto about 70 C. for one-half hour. A solution of 1 part oleic acid in 104parts of the hydrocarbon liquid of example 14 was then stirred into theaqueous phase at 70 C. The coating was homogenized at 2,000 p.s.i.g. ina Manton- Gaulin Homogenizer. The coating contained 24 percent solidsand had a viscosity of 2,000 c.p.s. It was applied to a 50-pound(25X38-basis) coating raw stock at a level of 4 pounds per ream per sidewith a No. 10 wire-wound rod. The coated papers were supercalendered ata nip pressure of 400 pounds per lineal inch. The bubble-coated paperwas compared to a commercial -pound coated offset paper and the data areshown in table 1.

It will be seen from table 1 that the coating of this example equals thecommercially available coating in brightness, opacity and printingstrength while at the same time exhibiting improved gloss ink holdout.Most importantly, the coating weight was reduced by 2 pounds per ream.

16 COATED PAPER WITH OFFSET PAPER Basis n 1ST weig t p n ng (25 x 38-Percent 5 ink Printing 500) reflec- Percent strength, smooth- Gloss inkSample pounds tance opacity 2 I.p.m. ness holdout Coatllgng rawi siitck60 85 90 o xam e Example iii coated 58 85 92 370 Good. Excellent.

a er. C m inercial oil'set 60 85 93 360 .do. Good.

paper.

1 Measured with Photovolt brightness meter. 7 Measured by 'IAPPIStandard T425. 5 Measured 01 Print Testing Apparatus. i V Wm 7 solids)sold by Rohm & Haas Company as Amberlac 165. The EXAMPLE l7 last-namedresin is a matrix structure-forming component. Thus it will be seen thatthe ratio of the two types ofresin components had been altered toprovide relatively more of the matrix structure-forming resin system.This aqueous phase liquid was heated to 82 C. with gentle stirring.After dissolving 2 parts of oleic acid in 690 parts of the hydrocarbonliquid A styrene-maleic anhydride resin (Lytron 810 from MonsantoCompany) and a synthetic acrylic resin (AC-34 of Rohm & Haas Company)served as the matrix structure-forming a film-forming resins in aformulation made up as in examples 6-9. The weight ratio of resins was20/80 and the resultused in example ID, the oil phase solution wasemulsified in ing coating hadarefiectance of50 percent.

EXAMPLE 18 A commercially available blend which in essence comprises acombination of the first and second classes of blends was used. Oneembodiment of this blend is a sold as Lytron 5,202 by Monsanto Companyand the general type of blend is described in US. Pat. No. 3,396,135. itis available as a 40 percent solids latex and was used in this form bystirring in 80 parts of a liquid aliphatic hydrocarbon (distillationrange between 205and 258 C.) to give a ratio of binder of hydrocarbon ofl-to-2. The emulsion was refined so that the oil-phase globules rangedbetween one-tenth and six-tenth micron in diameter. The coating, appliedand dried as in example 14, had a reflectance of 80 percent.

This coating formulation was modified by the addition of pigment gradetitania in an amount equal to the weight of the resin solids to give acomposition in which the ratio of binder to pigment to water-immiscibleliquid was 1 to l to 2. The substrate for coating was cedar clapboardhaving one coat of an oil-base primer. For comparison, a first portionof the primed substrate was left unpainted, a second portion was coatedby brushing on one coat of the composition of this example and a thirdportion was coated by brushing on an essentially equal weight of acommercially available white latex paint. After drying, the reflectancesof the three portions were measured using a green filter to obtain thefollowing measurements:

Primed surface Primed surface with commercial paint Primed surface withexample 18 coating EXAMPLE 19 The hard, nonfilm-forming polymer latex ofexample 2 was used with two different coalescing agents, namely N-methyipyrrolidone and diacetone alcohol. in each formulation, 100 parts of thelatex, parts of the coalescing agent and 90 parts of a petroleumfraction (distillation range of 205to 258 C.) were used. The coalescingagent as a 50 percent aqueous solution was added to the latex and themixture allowed to stand overnight. The petroleum fraction was thenadded with mechanical stirring and some water (about 50 parts) was addedto reduce viscosity. The mixtures were then processed in a Manton-Ganlinl-lomogenizer at zero gauge pressure and the coatings cast at the rateof approximately 600 square feet per gallon on contrast ratio cards.These formulations produced coatings of approximately 40 percentbrightness as judged visually.

EXAMPLE 20 A modified acrylic latex (40 percent solids) (sold as Lytron116 by Monsanto Company) and being characterized as a relatively hardpolymer was added in 100 parts to a mixture of 7.5 parts propylenecarbonate in 7.5 parts water. Then 80 parts of the hydrocarbon ofexample 19 was added with stirring. The resulting emulsion was processedat 500 psi. in the Manton-Gaulin Homogenizer and coatings were cast onblack cardboard at the rate of approximately 600 square feet per gallonand allowed to air dry overnight. A reflectance of 85 percent wasobtained.

The two types of resin components making up the blend used as the bindersystem must meet certain physical requirements. The matrixstructure-forming resin or resin system must be a relatively hard resinwhich exhibits essentially no creep in film form and little elasticity.It may or may not be a film former; and if its does not form a film itscreep may be evaluated by adding a small amount of a suitableplasticizer to form a test film. After the coating composition of thisinvention is applied to a substrate surface and as the water from thecontinuous phase is removed, the matrix structure forming resin orresins must be capable of hardening or setting up to form aself-supporting structure to retain the water-immiscible globules inessentially the same spatial relationship as they 0c cupied in theliquid emulsion coating. Finally, this resin component must becompatible with the film-forming resin component, i.e., not precipitatedby it in the coating composition or during drying, and also essentiallyinert to the water-immiscible liquid. It may be soluble or dispersiblein the water of the aqueous phase. in addition to the use of caseinwhich is a natural resinous material, many synthetic resin groupings,e.g., styrene and maleic anhydride, are suitable for this component.

The second or film-forming resin component must first, of course, becapable of forming a film. It will generally be a soft film incomparison with the matrix structure-forming resin and may exhibit awide range of toughness and pressure sensitivity. It will preferablyexhibit minimal creep and elasticity. The choice of the film-formingresin component will be determined at least to a great extent by theproperties desired in the final coating. As an example of this componentwe may cite resins containing the acrylic grouping.

The ratio of the two resin components will depend upon the resins usedand the properties (reflectance or brightness, pressure-sensitivity,surface characteristics, etc.) required in the final coating. In anycomposition there must be a sufficient quantity of the matrix-structureforming resin to support the final bubble structure as represented bythe attainment of at least 40 percent reflectance for a standard coatingweight.

The reflectance data from the examples, along with data on creep,percent elongation and stress for the binders are summarized in table 2.From these data it is possible to define resin weight ratios and thephysical properties required of the blend of resin components which goto make up the coating b der;

TABLE 2.RELATIONSHIP BETWEEN REFLECTANCE AND PHYSICAL PROPERTIES OFBINDER SYSTEM Weight ratio of matrix structure- Percent 01 forming toStress Example film-forming Reflec Creep Elonratio Number resin tance(25 g.) gation at 10% l Mechanically weak film.

3 Not precisely determlnublo-seo Examples.

a Contained coalescing agent.

Extended experience with these bubble coatings has shown that coatingswith reflectances between 40 and 50 percent using the coating weightsspecified are of marginal accepta: bility and those with reflectancesbelow 40 percent cannot be classified as satisfactory bubble coatings.

The resins making up the binder of the coating must in combinationexhibit low creep and preferably a relatively low percentage ofelongation and a relatively high stress ratio. In order to determinethese properties the resins are blended in the same weight ratio as theyare to be present in the final bubble coating. Then a film of the resinblend is cast and used to detennine the properties of the blend in filmform without any air-binder interfaces.

Creep which is essentially a measure of cold flow under load isdetermined by cutting a 96 inch wide strip from the film, making twomarks on the film a known distance apart and then firmly attaching oneend by means of a clamp. A 25-gram weight is then affixed to the freeend and after 16 hours at room temperature the distance between the twospaced marks is again measured. The percent increase in this distancebetween the marks (corrected for a 1 mil thick film) is the presentcreep. For purposes of a satisfactory bubble coating the resin blendmust have a creep below about 250percent, more desirably below about 150percent and preferably one which approaches zero.

Percent elongation data for the cast films of the resin blends making upthe binder were obtained on the standard Instron tester. The dataobtained are measurements of the increase in the length of a film stripwhen it is pulled until it breaks. This percent elongation may vary tosome extent depending upon the coating use. However, it is desirablethat it should not be greater than 300 percent for the binder system andit is preferable that it be considerably less than 300 percent, e.g.,less than about 200 percent.

Stress ratios are calculated from stress plots by the following formulaStress required for elongation VA Stress required to break strip X Ingeneral, the higher this stress ratio the less elastic is the film andthe more desirable is the binder system for bubble coatings. lt ispreferred that this ratio by greater than 25 for a binder system of thisinvention. However, this property is essentially a restatement ofelongation and it is generally preferable to be guided by the latter.

The liquid forming the discontinuous phase of the emulsion must be awater-immiscible organic liquid, the bulk of which has a boiling rangeabove that of water at the drying temperature required. Moreover, at theinitial drying temperature, the discontinuous phase liquid must have avapor pressure below that of water in order to permit the first portionof the water to be removed to set up the matrix structure-forming resinwithout any substantial removal of the organic liquid. Suitablewater-immiscible organic liquids include, but are not limited to,aliphatic hydrocarbons, commercial petroleum fractions, xylene,kerosene, mineral spirits, high flash naphthas, ketones such as butylmethyl ketone and amyl ethyl ketone, paraffin hydrocarbons such asoctane, and the higher-boiling acetates such as butyl acetate or amylacetate.

The final choice of the liquid forming the discontinuous phase may alsorequire the consideration of such factors as that which will give thebrightest coating for a given weight per unit area of surface for aspecific film-forming material; that which will prove to be the mostcompatible with other components such as a hinder, the dispersing agentand any particulate additive, dye or dyes added; and that which willmeet certain other requirements such as toxicity, infiammability,adaptability to production procedures, cost and the like.

Inasmuch as the mixing of the coating composition of this inventionrequires a thorough dispersing of one liquid in another, each of whichis essentially immiscible in the other, it may be desirable to add adispersing agent such as those commonly to prepare emulsions if it isnot already present in any commercially available latex used. Such adispersing agent may be one of the appropriate soaps such as ammonium,sodium or potassium oleate or stearate or other suitable emulsifyingagents. The dispersing agent may be formed in situ by a reaction betweena weak organic acid and an alkali metal ion furnished, for example, froman excess of solubilizing agent. Thus, if stearic acid is added to acoating mixture containing an excess of ammonium ions, ammonium stearateis formed and serves as a dispersing agent.

Generally, the weight ratio of binder material (formed of the resinblend, to the liquid of the discontinuous phase will range from aboutl-to- 0.25 to about l-to-S. The actual ratio will depend upon thecharacteristic of the final coating desired. As a rule, the smalleramount of binder material, the higher the brightness of the finalcoating, a preferred ratio being from about l-to-l to l-to-S forpressure-sensitive coatings, and from about l-to-0.25 to l-to-2 forpressure-sensitive coatings.

In preparing the binder solution, or dispersion, it has been founddesirable to formulate solutions having from about 5 percent to about 40percent solids content by weight, the higher solids content solutionsbeing generally preferred since they decrease the ultimate drying loadand increase the rate of drying.

One or more particulate additives may be incorporated in the coating ofthis invention. Such finely divided particulate materials are generallyof inorganic origin and inert to the binder material as well as to thediscontinuous phase liquid under the condition which the coating isapplied to the substrate. The particulate matter is preferably sizedfiner than 12 microns; however, particle sizes up to those which can besubstantially permanently bonded by the binder system may be used. Thefinal surface characteristics of the coating will control the size ofthe particulate matter; thus, if a coarse surface is undesirable, thenthe particulate matter will be sized within the finer size range.

It is important to note that the particulate additive used in thecoating of this invention is generally not present in the role of apigment insofar as the term pigment is used generally to denote amaterial which contributes opacity to a system. On the contrary, it canbe shown that although many of the particulate additives can in somecoatings and size ranges be considered pigments, they usually contributeless brightness or opacity to the coating of this invention; rather theycontribute desirable properties to the surface of the coating. in someinstances, the particulate matter actually somewhat reduces opacity andbrightness for a given coating weight. The particulate additive may befurther characterized as a material which is substantially wetted byeither the water solution of the matrix material or by the discontinuousphase liquid and which can be permanently bonded within the final matrixfilm. The particulate additive may also possess other more specificcharacteristics such as being highly absorbent to the liquid medium ofthe ink used in printing, or the capability of imparting modification inthe appearance of the surface such as a metallic appearance which wouldbe created by the use of finely divided aluminum powder or flakes as aparticular additive.

Typical particulate additives include, but are not limited to, chalk,clay, titania silica, hydrated calcium silicate, metallic powder such asaluminum and bronze, carbon black and dye pigments such as anultramarine blue and the like. The amount of particulate additive whichmay be added may be as high as about 3 to 4 times the weight of thetotal resins forming the binder. Generally, for making coatings suitablefor printing, it will be preferable to the use weight ratios of binderto particulate additive of from about 120.5 to 1:4.

in mixing the coating composition of this invention, it is desirable tomake up the binder solution containing the resin blend and particulateadditive separately, and then while stirring add the discontinuous phaseliquid containing any dispersing agent. Dyes and other additives may beincorporated into either of the emulsion phases. Subsequent to theformation of the emulsion, it may be necessary to further process theemulsion to adjust the size range of the discontinuous phase globule,that is, of the globules of the water-immiscible organic liquid makingup this discontinuous phase. This may be done by any known techniquesuch as passing the emulsion through a homogenizer. inasmuch as the sizerange of the globules making up the discontinuous phase of the emulsionis later to determine the size range of the interfaces in the finisheddry coating, it is necessary to make this adjustment so that essentiallyall of the discontinuous phase globules range in size from aboutone-tenth to 1 micron with no appreciable number exceeding 5 microns.

Once the coating has been thoroughly mixed it is applied to thesubstrate by any well-known coating technique, and in the case ofpublication paper by high-speed coating apparatus, e.g., a trailingblade coater. It is not necessary to completely dry the substrate, i.e.,paper or wall prior to the application of the coating. Thus, if thecoating is to be applied to paper the coating may be an on-machineoperation during the actual manufacturing of the paper. Generally, inthis case the emulsion coating is applied at a temperature of betweenabout 33 and 38 C. in keeping with high-speed coating techniques.However, it may be applied over a wide temperature range (e.g., fromambient temperature up to 65 C.) so long as the temperature ismaintained relatively constant.

The coating composition of this invention may be applied to a widevariety of surfaces or substrates. These include, but are not limitedto, tissue paper, publication paper raw stock, paperboard, wood,plaster, plastics and metal. As noted above and as shown in theexamples, the coating may be formulated to exhibit a wide range ofphysical properties, the choice being indicated by the surface to becoated and the use for which the coating is to serve. Such a choice iswithin the knowledge of those skilled in the coating art.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above composition and articlewithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

We claim:

1. A coated article comprising a substrate carrying adhered thereto andopaque binder in substantially continuous film form, said binder filmbeing characterized as a dried, essentially uncollapsed residue of anemulsion wherein the continuous phase of said emulsion becomes saidbinder which comprises a blend of an essentially nonelastic resinfilm-forming component and a matrix structure-forming component which isrelatively hard compared with said film-forming component, possessesessentially no creep and little elasticity in film form, is capable ofhardening to form a self-supporting structure and is compatible withsaid film-forming component, said binder film being furthercharacterized as having distributed throughout its entire volumemultitudinous air-binder interfaces, the sizes of which aresubstantially equivalent to the globules making up the discontinuousphase of the original emulsion, and essentially all of which vary inmaximum dimension from about one-tenth to 1 micron with no appreciablenumber exceeding 5 microns, thereby providing a uniformly cavernuloussubstantially continuous structure having a reflectance of at least 40percent; said binder in a nonbubble film form having a creep at ambienttemperature under a 25- gram load of no more than 250 percent correctedfor l-mil thickness, an elongation less than 300 percent and a 10percent stress ratio greater than 25.

2. An article in accordance with claim 1 wherein said blend comprises anemulsion polymerized styrene homopolymer serving as said matrixstructure-forming component and an emulsion polymerized styreneinterpolymer, serving as said film-forming component.

3. An article in accordance with claim 1 wherein said blend comprises astyrene-maleic anhydride resin and a homogeneous blend of an emulsionpolymerized styrene homopolymer and an emulsion polymerized styreneinterpolymer, the

styrene of said styrene-maleic anhydride resin and said styrenehomopolymer serving as matrix structure-forming components and themaleic anhydride of said styrene-maleic anhydride resin and said styreneinterpolymer serving as said film-forming components.

4. An article according to claim 1 wherein said binder in film form onsaid substrate is pressure sensitive and said substrate is of a colordifferent from said binder.

5. An article in accordance with claim 1 wherein said binder in filmform on said substrate is relatively pressure insensitive.

6. An article in accordance with claim 1 wherein said substrate ispublication paper raw stock.

7. An article in accordance with claim 1 wherein said substrate ispaperboard.

8. An article in accordance with claim 1 wherein said blend comprises aphysical mixture of at least one matrix structureforming resin and atleast one film-forming resin.

9. An article in accordance with claim 1 wherein said matrixstructure-forming component comprises casein.

10. An article in accordance with claim 1 wherein said matrixstructure-forming component contains a styrene grouping.

11. An article in accordance with claim 1 wherein said filmformingcomponent contains an acrylic grouping.

12. An article in accordance with claim 1 wherein said matrixstructure-forming component contains a maleic anhydride grouping.

13. An article in accordance with claim 1 further characterized byhaving finely divided particulate material uniformly distributedthroughout said binder.

2. An article in accordance with claim 1 wherein said blend comprises anemulsion polymerized styrene homopolymer serving as said matrixstructure-forming component and an emulsion polymerized styreneinterpolymer, serving as said film-forming component.
 3. An article inaccordance with claim 1 wherein said blend comprises a styrene-maleicanhydride resin and a homogeneous blend of an emulsion polymerizedstyrene homopolymer and an emulsion polymerized styrene interpolymer,the styrene of said styrene-maleic anhydride resin and said styrenehomopolymer serving as matrix structure-forming components and themaleic anhydride of said styrene-maleic anhydride resin and said styreneinterpolymer serving as said film-forming components.
 4. An articleaccording to claim 1 wherein said binder in film form on said substrateis pressure sensitive and said substrate is of a color different fromsaid binder.
 5. An article in accordance with claim 1 wherein saidbinder in film form on said substrate is relatively pressureinsensitive.
 6. An article in accordance with claim 1 wherein saidsubstrate is publication paper raw stock.
 7. An article in accordancewith claim 1 wherein said substrate is paperboard.
 8. An article inaccordance with claim 1 wherein said blend comprises a physical mixtureof at least one matrix structure-forming resin and at least onefilm-forming resin.
 9. An article in accordance with claim 1 whereinsaid matrix structure-forming component comprises casein.
 10. An articlein accordance with claim 1 wherein said matrix structure-formingcomponent contains a styrene grouping.
 11. An article in accordance withclaim 1 wherein said film-forming component contains an acrylicgrouping.
 12. An article in accordance with claim 1 wherein said matrixstructure-forming component contains a maleic anhydride grouping.
 13. Anarticle in accordance with claim 1 further characterized by havingfinely divided particulate material uniformly distributed throughoutsaid binder.